1. Field of the Invention
The present invention relates to a super luminescent diode, and more particularly, to a 2-section super luminescent diode in which a super luminescent diode and an optical amplifier are formed as a single platform.
This work was supported by the IT R&D program of MIC/IITA [2006-S-073-02, Nano flexible opto-electric PCB module for portable display].
2. Discussion of Related Art
To construct a cost-effective Wavelength Division Multiplexing (WDM) subscriber network system, it is essential to develop a stable and cost-effective light source. Particularly, as every subscriber in the WDM subscriber network system is assigned a specific wavelength for communication, it is necessary to have a wavelength-independent light source capable of providing the same light source to the subscribers regardless of the assigned wavelength.
Various wavelength-independent light sources have been actively studied, such as a wavelength locked Fabry Perot-laser diode (WLFP-LD), a reflective semiconductor optical amplifier (RSOA), and a planar light wave circuit-external cavity laser (PLC-ECL).
A re-modulation structure employing the WLFP-LD and the RSOA has disadvantages of being dependent upon properties of the light source and being limited to a data rate of 1.25 Gb/s for direct modulation.
Accordingly, the PLC-ECL has drawn attention as a light source of a WDM optical subscriber network because of being cost-effective and having possibility of over 2.5 Gb/s transmission by direct modulation.
The grating of ECL structure is formed on silica and polymer waveguides on a silicon substrate and a semiconductor light source is hybrid integrated.
It is required for the semiconductor light source of the ECL not to oscillate with a reflectance of no more than 0.1% at an output facet and to have a high output in low current operation.
A Fabry Perot-laser diode (FP-LD) and a super luminescent diode (SLD) both meet these requirements. However, the SLD is widely used because of its wide bandwidth.
In a typical SLD, an active layer or an optical waveguide is tilted by 7 or 10 degrees to reduce a reflectance of an output facet. Even though such an SLD may have a reduced reflectance of the output facet, it is not suitable for a WDM-passive optical network (PON) due to increase in threshold current and operation current. Accordingly, research is actively underway into an SLD light source having properties comparable to a Fabry-Perot with anti-reflection and high reflection coatings.
Meanwhile, for a high-output SLD, integration of an SOA into the SLD has been researched. Recent research has revealed that the SLD integrated with SOA nearly doubles the output power of the SLD. Such an SLD is inappropriate for a PLC-ECL and particularly a PLC-ECL for a WDM-PON because of its overly high threshold current.
Thus, there is need for an SLD with a lower threshold current and a nearly double output of a typical SLD.